Metals for Bus Bars

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NSW Annual Seminar and Exhibition

Metals for Busbars

Alex GouchTechnical Manager

Austral Wright Metals

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Metals for Busbars

• Why copper ?• Copper conductor metallurgy• The proof of the pudding

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Copper for BusbarsWhy copper ?

– Aluminium is much cheaper– Overhead conductors are now mostly aluminium– Copper has

• Better electrical properties• Better mechanical properties• Better thermal properties• Better corrosion resistance• Better ease of fabrication• Uses smaller cabinets• Reliable, long lasting connections

– Copper busbars give a more reliable result

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CopperC11000

Aluminium AA1350 Units

Electrical conductivity (annealed) 101 61 % IACS

Electrical resistivity (annealed) 1.72 2.83 µΩ cm

Temperature coefficient of resistance (annealed) 0.0039 0.004 /° C

Thermal conductivity at 20° C 397 230 W/mK

Coefficient of expansion 17 x 10-6 23 x 10-6 /° C

Tensile strength (annealed) 200 - 250 50 - 60 N/mm²

Tensile strength (half-hard) 260 - 300 85 - 100 N/mm²

0.2% proof stress (annealed) 50 - 55 20 - 30 N/mm²

0.2% proof stress (half-hard) 170 - 200 60 - 65 N/mm²

Elastic modulus 116 - 130 70 kN/mm²

Specific heat 385 900 J/kg K

Density 8.91 2.70 g/cm³

Melting point 1083 660 °C

1 N/mm2 = 1MPa

At the same DC resistance the weight of an aluminium conductor is about half that of a copper conductor.

Electrical Properties & Price

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CopperC11000

Aluminium AA1350 Units

Electrical conductivity (annealed) 101 61 % IACS

Electrical resistivity (annealed) 1.72 2.83 µΩ cm

Temperature coefficient of resistance (annealed) 0.0039 0.004 /° C

Thermal conductivity at 20° C 397 230 W/mK

Coefficient of expansion 17 x 10-6 23 x 10-6 /° C

Tensile strength (annealed) 200 - 250 50 - 60 N/mm²

Tensile strength (half-hard) 260 - 300 85 - 100 N/mm²

0.2% proof stress (annealed) 50 - 55 20 - 30 N/mm²

0.2% proof stress (half-hard) 170 - 200 60 - 65 N/mm²

Elastic modulus 116 - 130 70 kN/mm²

Specific heat 385 900 J/kg K

Density 8.91 2.70 g/cm³

Melting point 1083 660 °C

1 N/mm2 = 1MPa

Mechanical Properties

Copper much easier to handle in the workshop

Copper more robust

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Material Testing Temp. °C

Min. Creep Rate % per 1000 h

Stress MPa

Aluminium (1080) annealed 20 0.022 26

HC Cu annealed 150 0.022 26

Creep

Material Fatigue strength N/mm²

No. of cycles x 106

HC Aluminium annealed 20 50

half-hard (H8) 45 50

HC Copper annealed 62 300

half-hard 115 300

Fatigue

Copper is much less likely to fail at bolted connections by creep or stress relaxation.

Copper more tolerant of higher operating/fault temperatures.

Copper better able to withstand repeated mechanical stresses.

Mechanical Properties

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CopperC11000

Aluminium AA1350 Units

Electrical conductivity (annealed) 101 61 % IACS

Electrical resistivity (annealed) 1.72 2.83 µΩ cm

Temperature coefficient of resistance (annealed) 0.0039 0.004 /° C

Thermal conductivity at 20° C 397 230 W/mK

Coefficient of expansion 17 x 10-6 23 x 10-6 /° C

Tensile strength (annealed) 200 - 250 50 - 60 N/mm²

Tensile strength (half-hard) 260 - 300 85 - 100 N/mm²

0.2% proof stress (annealed) 50 - 55 20 - 30 N/mm²

0.2% proof stress (half-hard) 170 - 200 60 - 65 N/mm²

Elastic modulus 116 - 130 70 kN/mm²

Specific heat 385 900 J/kg K

Density 8.91 2.70 g/cm³

Melting point 1083 660 °C

1 N/mm2 = 1MPa

Thermal Properties

Copper less liable to hot spots.

Copper needs less support.

Copper less prone to thermal fatigue failure.

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Self-extinguishing arcs in copper and aluminium busbars

Copper Aluminium

Minimum busbar spacing, mm 50 100

Maximum current per busbar, A 4,500 3,220

Thermal Properties

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Contact Properties

• Copper has better corrosion resistance.

• Copper corrosion products are more conductive.

• Copper contacts are more forgiving.

Copper contacts are much more reliable in the long run

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28%

12% 9%9%

42%

Electrical/ElectronicConstructionTransportConsumer/GeneralIndustrial Machinery

Copper & Aluminium Use

Copper

17,974,300 tonnes (2007)

22%

26%

14% 8%

22%8%

Electrical/ElectronicConstructionTransportConsumer/GeneralIndustrial MachineryPackaging

Aluminium

38,108,700 tonnes (2007)

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Busbar Materials

• Why copper ?• Copper conductor metallurgy• The proof of the pudding

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IACS

• International Annealed Copper Standard– Standardised in 1913– Volume resistivity = 1.7241 m.Ω.cm

• Materials standards written around 97% IACS– Allows use of hard-drawn C11000

• Modern HC copper is typically 101.5% IACS

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Copper for Conductors

Conductivity

%IACS

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Effect of cold work

Hard drawn busbar only loses about 2 – 3% IACS.

C11000

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Grades of Copper

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Oxygen

Other

100% IACS>99.95%Oxygen freeC10200

100% IACS>99.90%ETPHC

C11000

ConductivityMinimum

(Annealed)CopperNameAlloy

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Busbar Purity

• Feed for meltshop can be cathode, electrowon or electrical scrap

• Purest is cathode

– Purest of all is ISA Cathode

• Riskiest is electrical scrap

– Gloves, nails, tube, coke cans etc

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OC-ETP® Copper vs Others

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5

10

15

20

25

97.0

97.5

98.0

98.5

99.0

99.5

100.

0

100.

5

101.

0

101.

5

102.

0

102.

5

103.

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103.

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Standard Busbar OC-ETP Busbar

Conductivity, %IACS

Frequency

Oriental Copper maintain this standard –only use best quality cathodes

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Softening in service

Metals soften when they recrystallise.

There is a recrystallisation temperature, which varies a little depending on the prior cold work.

TensileStrength,MPa

Elongation,%

Conductivity,% IACS

C11000

Annealing temperature, oC

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Making BusbarsRaw material -cathode

Reheat Colddraw

Melt

Cast

Extrude

Underwater runout

Busbar

[Tin Plate]

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Extrusion Process

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Bending• Effect of Copper Structure

Copper Grain Size

Bending of OC-ETP® : Smooth surface Bending of other copper 1 : Orange peel

Microstructure of OC-ETP®

(Grain size = 25 microns)Microstructure of other copper 1

(Grain size = 75 microns)

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Where to use tin plated Climate (Temperature / Humidity) Acidic or Alkaline condition Chloride / Sea water condition Industrial / Polluted area condition

If subject to bad environment, the use of Tinplated Copper Busbar is required.

Bare Copper Busbars Tinplated Copper Busbars

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Busbar Materials

• Why copper ?• Copper conductor metallurgy• The proof of the pudding

So what ? – Effect of higher %IACS

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Thank you for your attention

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